Bending, hydration and interstitial energies quantitatively account for the hexagonal-lamellar-hexagonal reentrant phase transition in dioleoylphosphatidylethanolamine

Abstract

We have accounted for the unusual structural change wherein dioleoylphosphatidylethanolamine undergoes a hexagonal-lamellar-hexagonal transition sequence as the water content is reduced systematically. We describe the role played by the energies of bending, hydration, voids in hexagonal interstices, and van der Waals interaction in this transition sequence. We have used the X-ray diffraction and osmotic stress experiments on the two phases to derive the structural parameters and all of the force constants defining the energetics of the hexagonal and lamellar phases. We have calculated the chemical potentials of lipid and water in both phases and derived the phase diagram of the lipid with no free, adjustable parameters. The calculated temperature/osmotic stress and temperature/composition diagrams quantitatively agree with experiment. The reentrant transition appears to be driven by a delicate balance between the hydration energy in the lamellar phase and bending energy in the hexagonal phase, whereas the energy of voids in hexagonal interstices defines its energy scale and temperature range. Van der Waals attraction between the bilayers in the lamellar phase does not appear to be important in this transition.

Modulation of CTP:phosphocholine cytidylyltransferase by membrane curvature elastic stress

“…Because it is quite likely that in fact the more stressed lipids will aggregate around the CCT, we must accept the approximate nature of the model. Reliable experimental values of c 0 , , and A are known for DOPC and DOPE (25,26,32,34) (Table 1), and we are therefore able to fit S (x) for mixtures of these lipids (Fig. 2).…”

“…Adding DOPE to DOPE͞DOPC vesicles also increases the desire for curvature toward the water, but now it is because of the lower hydrophilicity of the phosphatidylethanolamine headgroup (33). However, the consequent increase in is therefore accompanied by a reduction in A to approximately 69 Å 2 at 60 mol% DOPE (25). This means that as we travel from left to right in Fig.…”

“…For the type II lipid amphiphile, dioleoylphosphatidylethanolamine (DOPE), we calculate that the total stored curvature elastic energy for each DOPE molecule in a flat monolayer is approximately 1 k B T (23,25,26). Qualitatively, we can see that the partial submersion of the amphipathic ␣-helical binding domain of CCT into an amphiphilic monolayer allows the release of at least some of this stored curvature elastic energy for type II amphiphiles (Fig.…”

Directed Self-Assembly of Lipid Nanotubes from Inverted Hexagonal Structures

“…Next, we discuss the physics behind the self-assembly. On the basis of the previous theoretical study on DOPE, 40 …”

Elastic energy of tilt and bending of fluid membranes

“…While the description can be performed in terms of an arbitrary dividing surface [29], we use a particular one which separates the regions of the polar heads and the hydrocarbon chains. For several lipids this dividing surface plays the role of the neutral surface, for which the deformations of monolayer stretching and bending are energetically decoupled [30,31].…”